Answer
2.731 cm
Work Step by Step
$D_{new}=D+\Delta D$
As the equation for linear thermal expansion is applicable to diameters,
$\Delta D=D\alpha\Delta T$
Therefore, we can write
$D_{new}=D+D\alpha\Delta T=D(1+\alpha \Delta T)$
Given: $D=2.725\,cm$, $\Delta T=100.0^{\circ}C$,
Coefficient of linear expansion of Al=$23\times10^{-6}/C^{\circ}$
Result:
$D_{new}=2.725\,cm(1+23\times10^{-6}/C^{\circ}\times100.0^{\circ}C)$
$=2.731\,cm$
